
F-measure (FM):
\(FM = \frac{2\times Recall \times Precision}{Recall + Precision}\) 
where \(Recall=\frac{TP}{TP+FN}, Precision=\frac{TP}{TP+FP}\) , \(TP,FP,FN\)  denote the True positive, False position and False Negative values, respectively.

pseudo F-measure (\(F_{ps}\) ):
\(F_{ps} = \frac{2\times pRecall \times Precision}{pRecall + Precision}\) 
where \(pRecall\)  is the percentage of the skeletonized ground truth image described in [1]}.

distance reciprocal distortion metric (DRD):
\(DRD = \frac{\sum _k DRD_k}{NUBN}\) 
where \(DRD_k\)  is the distortion of the \(k\) -th flipped pixel and it is calculated using a 5\(\times \) 5 normalized weight matrix and \(NUBN\)  is the number of the non-uniform 8\(\times \) 8 blocks in the ground truth image (see details in [2]}).

peak signal-to-noise ratio (PSNR):
\(PSNR = 10\text{log}(\frac{C^2}{MSE})\) 
where \(MSE=\frac{\sum _{x=1}^M\sum _{y=1}^N(I_{bin}(x,y)-\hat{I}_{bin}(x,y))^2}{MN}\) , \(C\)  denotes the difference between the text and background.

